Evol Ecol Res 16: 417-433 (2014)     Full PDF if your library subscribes.

Relative contributions of evolutionary and ecological dynamics to body size and life-history changes of herring (Clupea harengus) in the Bothnian Sea

Örjan Östman1, Olle Karlsson2, Jukka Pönni3, Olavi Kaljuste1, Teija Aho1 and Anna Gårdmark1

1Department of Aquatic Resources, Swedish University of Agricultural Sciences, Öregrund, Sweden,  2Department of Environmental Research and Monitoring, Swedish Museum of Natural History, Stockholm, Sweden and  3Natural Resources Institute Finland, Natural Resources and Bioproduction, Helsinki, Finland

Correspondence: Ö. Östman, Department of Aquatic Resources, Swedish University of Agricultural Sciences, Skolgatan 6, SE-742 42 Öregrund, Sweden.
e-mail: orjan.ostman@slu.se

ABSTRACT

Question: What ecological and evolutionary processes are associated with the 25% decrease in age-specific body size of herring (Clupea harengus) in the Bothnian Sea over the last 30 years?

Data: Four decades of data on length, age, and sexual maturity of individual herrings as well as environmental variables, including abundances of predators, prey and competitors, and estimates of fishing intensity/mortality from the Bothnian Sea.

Search methods: Information-theoretic assessment of the relative influence of ecological and fisheries’ effects on temporal changes in body growth. Probabilistic maturation reaction norms to study changes in age-specific size at maturation. Decomposition of trait variation into ecological and evolutionary contributions.

Conclusions: Our evolutionary ecosystem perspective shows that both ecological and evolutionary processes are important contributors to observed phenotypic changes in this commercially exploited species. Around 60% of the decrease in age-specific body length can be attributed to increased density-dependent body growth. Evolutionary changes towards earlier maturation, owing to an indirect effect of size-selective mortality from grey seals and fisheries, account for a further 25% of the decrease in age-specific body size.

Keywords: Baltic Sea, density dependence, fisheries, grey seal, pelagic, zooplankton.

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